1. Field of the Invention
The present invention relates generally to data storage media and methods of manufacturing data storage media.
2. Description of the Related Art
FIG. 1 illustrates an ultra-high-density data storage device 10 according to the related art. The data storage device 10 is made up of a storage medium 20 and a tip wafer 30 positioned proximate to one surface of the storage medium 20. The storage medium 20 contains nanometer-scaled data bits 40 that are written to and read from the storage medium 20 by emitters 50 located on the surface of the tip wafer 30 closest to the storage medium 20. The writing and reading operations will be discussed below.
The emitters 50 bombard the data bits 40 with electron beams that are focused to nanometer-scaled spots. If the beams are of sufficiently high energy, the bombarded data bits 40 experience a phase change (e.g., between a crystalline and amorphous state). Effecting such a phase change constitutes writing to the storage medium 20.
In the data storage device 10 illustrated in FIG. 1, a number of nanometer-scaled data bits 40 are contained within the storage medium 20. If these data bits 40 have been written to by any of the emitters 50 as discussed above, they can be considered as data bits 40 that represent the number xe2x80x9c1xe2x80x9d. On the other hand, the data bits 40 that have not been written to can be considered to be data bits 40 that represent the number xe2x80x9c0xe2x80x9d.
Whether a data bit 40 represents a xe2x80x9c1xe2x80x9d or a xe2x80x9c0xe2x80x9d can be determined by bombarding the data bit 40 in question with a lower energy beam than is used in the writing operation and monitoring the interactions of the beam with the data bits 40. Performing such steps is known as xe2x80x9creadingxe2x80x9d from the storage medium 20.
An example of a reading operation includes bombarding the data bits 40 of the storage medium 20 with a low-energy electron beam that would not effectuate a phase change of the data bits 40 being bombarded. This exemplary reading operation also includes monitoring how the low-energy bombarding electrons interact with the data bit 40. When a crystalline data bit 40 gets bombarded, a different number of electron-hole pairs are generated than when the low-energy electron beam bombards an amorphous data bit 40. Hence, by monitoring the number of generated electron-hole pairs, it becomes possible to determine whether a data bit 40 represents a xe2x80x9c1xe2x80x9d or a xe2x80x9c0xe2x80x9d.
FIG. 2 illustrates a close-up view of the related art storage medium 20 used in the data storage device 10 illustrated in FIG. 1. According to FIG. 2, the storage medium 20 is made up of a substrate 60 and of a crystalline phase-change layer 70 formed on one surface of the substrate 60. Although not illustrated, the data bits 40 discussed above are written to and read from the crystalline, phase-change layer 70.
FIG. 2 shows that the surface of the crystalline phase-change layer 70 furthest from the substrate 60 contains a high degree of surface roughness. Typically, the surface roughness exceeds 4.0 nanometer root-mean-square (RMS). Among other drawbacks, a surface roughness of this magnitude makes it difficult to form data bits 40 that are of a consistent size and therefore limits the resolution of the data storage device 10.
According to the related art method of forming the crystalline phase-change layer 70 illustrated in FIG. 2, high-temperature deposition methods are used. However, under high-temperature conditions (e.g., about 300 degrees Celsius), the crystalline phase-change layer 70 formed on the substrate 60 develops the relatively rough surface illustrated in FIG. 2 and can have a granular surface morphology that is disfavored for ultra-high-density storage devices 10.
Surface roughness is disfavored at least because it causes the data bits 40 to vary in geometry and can lead to added signal noise when reading from the storage medium 20. Further, the high-temperature deposition of the crystalline phase-change layer 70 according to the related art can lead to the loss of volatile group VI elements such as selenium and tolerium (Se, Te) that are typically used in the storage medium 20.
According to one embodiment, a method of fabricating a data storage medium that includes forming a phase-change layer over a substrate, forming a thick capping layer over the phase-change layer, changing the phase-change layer from a first phase to a second phase, removing the thick capping layer, and forming a thin capping layer over the phase-change layer.
According to another embodiment, a data storage medium that includes a substrate, a phase-change layer positioned over the substrate, and a thin capping layer positioned over the phase-change layer, wherein a first surface of the phase-change layer is positioned closest to the thin capping layer and wherein the first surface of the phase-change layer has a root mean square (rms) surface roughness of less than 2 nanometers.